Neuronal pathways which mediate specific mechanisms of color vision will be studied in the retina of goldfish and marine teleosts and elasmobranchs. Electron microscopy will be employed to analyze the membrane structure of identified synaptic contacts and the connectivity patterns of cones, bipolar and horizontal cells. Uptake or binding of radioactively labeled putative neurotransmitters and synaptic blockers, and immunochemical assays and localization, will be employed to indicate which cells and synapses may employ or respond to acetylcholine, gamma-aminobutyric acid, and thyrotropin releasing hormone. Retinas of embryos and adult fish labeled with 3H-thymidine will be examined for analysis of neurogenesis and synaptogenesis by electron microscopy and autoradiography.